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PubMed2004

Exaggerated pigmented granulomatous reaction to the artificial joint implant mimics metastatic melanoma.

Total joint replacement is a common orthopedic procedure. An artificial joint implant may fail due to mechanical mishap and a granulomatous reaction can be induced by the artificial joint debris after the mechanical failure. We report a case of an exaggerated pigmented granulomatous tissue response to metallic artificial joint implant debris in a 72-yr-old male that was mistaken for metastatic melanoma. The mass was soft, pigmented, ill-defined, and located in the right inguinal region. Fine-needle aspiration revealed numerous black-pigment laden cells. The cellular features were frequently obscured by the heavy pigmentation. Occasional cells exhibited atypia and prominent nucleoli. There were also abundant extracellular irregular small black particles dispersed in the background. The diagnosis of melanoma involving a lymph node was made. Since there was no prior history of melanoma, it was presumed that this represented metastatic melanoma from an unknown primary. A subsequent exploration of the groin was performed with the intent to resect the disease. At exploration, the mass was found to be contiguous with the hip joint and the frozen section of the mass revealed no evidence of melanoma. The final tissue diagnosis confirmed the frozen section report and showed a granulomatous reaction. This report underscores the diagnostic dilemma associated with the exaggerated pigmented granulomatous reaction due to an artificial prosthesis.

Aged↗
PubMed2001

Variegated expression and delayed retinal pigmentation during development in transgenic mice with a deletion in the locus control region of the tyrosinase gene.

Deletion of the tyrosinase locus control region (LCR) in transgenic mice results in variegated expression in the skin. Here we investigate the pigmentation pattern of other tissues that express tyrosinase: iris, choroid, and retina in the same animals. A mosaic distribution of pigmentation appears in the iris and choroid. Interestingly, a markedly different mosaic pattern is found in the retina, where central areas contain little or no melanin while pigmentation rises to normal levels towards periphery. Further, there is a temporal delay in the initiation and accumulation of pigment in retinal pigmented epithelium (RPE) cells during development, and patterns of adult retinal melanisation in these mice appear arrested at a stage found in early embryogenesis in wild-type mice. These results demonstrate that the tyrosinase LCR is needed for the correct establishment and maintenance of this expression domain throughout development, but particularly during the later stages of retinal melanisation.

Alleles↗
PubMed2001

Retinal photoreceptors and visual pigments in Boa constrictor imperator.

The photoreceptors of Boa constrictor, a boid snake of the subfamily Boinae, were examined with scanning electron microscopy and microspectrophotometry. The retina of B. constrictor is duplex but highly dominated by rods, cones comprising 11% of the photoreceptor population. The rather tightly packed rods have relatively long outer segments with proximal ends that are somewhat tapered. There are two morphologically distinct, single cones. The most common cone by far has a large inner segment and a relatively stout outer segment. The second cone, seen only infrequently, has a substantially smaller inner segment and a finer outer segment. The visual pigments of B. constrictor are virtually identical to those of the pythonine boid, Python regius. Three different visual pigments are present, all based on vitamin A(1.) The visual pigment of the rods has a wavelength of peak absorbance (lambda(max)) at 495 +/- 2 nm. The visual pigment of the more common, large cone has a lambda(max) at 549 +/- 1 nm. The small, rare cone contains a visual pigment with lambda(max) at 357 +/- 2 nm, providing the snake with sensitivity in the ultraviolet. We suggest that B. constrictor might employ UV sensitivity to locate conspecifics and/or to improve hunting efficiency. The data indicate that wavelength discrimination above 430 nm would not be possible without some input from the rods.

Animals↗
PubMed2006

Ascidian neural crest-like cells: phylogenetic distribution, relationship to larval complexity, and pigment cell fate.

Migratory neural crest-like cells, which express the cell surface antigen HNK-1 and develop into pigment cells, have recently been identified in the ascidian Ecteinascidia turbinata. Here we use HNK-1 expression as a marker to determine whether neural crest-like cells are responsible for pigment development in diverse ascidian species. We surveyed HNK-1 expression and tyrosinase activity in 12 ascidian species, including those with different adult organizations, developmental modes, and larval sizes and complexities. We observed HNK-1 positive cells in every species, although the timing of HNK-1 expression varied according to the extent of larval complexity. HNK-1 expression was initiated during the late tailbud stage in species in which adult features are formed precociously in large complex larvae. In contrast, HNK-1 positive cells did not appear until the swimming tadpole or juvenile stage in species with small simple larvae in which most adult features appear after metamorphosis. Double labeling experiments indicated that HNK-1 and tyrosinase are expressed in the same subset of pigment-forming mesenchymal cells in species with complex or simple larvae. In addition, the absence of HNK-1 and tyrosinase expression in albino morphs of the colonial ascidian Botryllus schlosseri suggested that the major fate of neural crest-like cells is to become pigment cells. The results suggest that ascidian neural crest-like cells and vertebrate neural crest cells had a common origin during chordate evolution and that their primitive function was to generate body pigmentation.

Animals↗
PubMed1979

Photomechanical migrations of pigment granules along the retinula cells of the crayfish.

The light-dependent migrations of proximal pigment granules along the photoreceptors of the crayfish compound-eye were studied in isolated retinas and eyestalks. The extent and kinetics of movement in each direction were found quantitatively equivalent to those observed in the organ in situ. These and other features make these cells to appear as intrinsically independent pigmentary effectors, directly responsive to light. During dark adaptation (DA) the pigment migrates away from the cell nucleus and accumulates along the axon in two distinct steps. Each step constitutes half of the total distance of about 180 microns and proceeds at 0.30 micron/sec. Only prolonged metabolic impairment inhibited the first phase, while the second was blocked by hypoxia, cyanide, colchicine, and D2O. The maintenance of a full DA position was also shown to be highly dependent upon metabolism. Light incidence on DA eyes is followed by an apparently monophasic expansion of the pigment from the axon towards the perikaryl region at 0.38 micron/sec. This movement was not affected by any of the foregoing agents and seems to be a passive relaxation process. Cytochalasin B had no effect on either motion. The migration in either direction has an exponential time course and is temperature dependent. Electron microscopy revealed two separate patterns of cytoplasmic organization corresponding to the cell areas where the two phases of DA occur. In the region close to the nucleus the pigment appears irregularly scattered, whereas in the axon the granules are situated arond a thick longitudinal bundle of microtubules. These results suggest the existence of two different mechanisms of pigment granule translocation operating in two separate regions of the retinula cell.

Animals↗
PubMed1998

Cloning and expression of a Xenopus short wavelength cone pigment.

The short wavelength visual pigment from Xenopus responsible for vision in the blue/violet portion of the spectrum was characterized by sequence spectroscopic analysis. The amino acid sequence was deduced by sequencing clones isolated by reverse transcription PCR, from retinal cDNA and genomic libraries. The gene contains 5 exons spanning 8.4 kb of genomic DNA and produces an mRNA of 2.4 kb in length. The deduced amino acid sequence predicts a protein of 347 amino acids with 76-78% identity to other short wavelength opsins. The mRNA encoding the Xenopus violet pigment was detected using in situ hybridization in cones, comprising a few percent of the total photoreceptors in the adult retina. The Xenopus violet opsin cDNA, modified to contain an epitope from the carboxyl terminus of bovine rhodopsin, was expressed in COS1 cells by transient transfection and analysed by UV-visible absorption spectroscopy. The protein expressed in COS1 cells migrated at 34 kD and was glycosylated at a single site in the amino terminus, exhibiting a diffuse pattern on SDS PAGE similar to bovine rhodopsin expressed in COS1 cells. Following incubation with 11-cis retinal, a light-sensitive pigment was formed with the lambdamax=425+/-2 nm. A Schiff base linkage between retinal and the violet opsin was demonstrated by acid denaturation. Xenopus violet opsin was sensitive to hydroxylamine in the dark, reacting with a half-time of 5 min at room temperature. This is the first group S pigment for amphibians. The pigment was expressed and purified from COS1 cells in a form that has permitted for the first time determination of the extinction coefficient, reactivity to hydroxylamine and presence of a Schiff base.

Amino Acid Sequence↗
PubMed1999

Retinal pigment epithelial cells are heterogeneous in their expression of MHC-II after stimulation with interferon-gamma.

The pattern of interferon-gamma-induced major histocompatibility complex Class II antigen expression was evaluated on the retinal pigment epithelium. Experiments were performed in vitro using explant cultures of aged and fetal human eyes and in vivo in albino rabbits. The human explants were stimulated with 50 U ml-1 interferon-gamma for 3 days prior to immunostaining for Class II. The rabbit eyes were subretinally injected in vivo with 50 microl of interferon-gamma (500 U ml-1) and analyzed immunohistochemically 3 days later. A heterogeneous pattern of Class II expression was present in the interferon-gamma-stimulated retinal pigment epithelial cells, in both the in vivo and the in vitro experiments. In aged human eyes the percent of Class-II positive cells was higher in the periphery than in the posterior pole (macular region) after interferon-gamma stimulation (P<0.01). No such difference was found in the fetal eyes. These data demonstrate that retinal pigment epithelial cells are heterogeneous in their response to interferon-gamma. The results are supportive of previous studies demonstrating the structural and proliferative heterogeneity of the retinal pigment epithelium. Together, these studies provide support for the possibility of functional retinal pigment epithelial heterogeneity.

Aged↗
PubMed1999

Transthyretin localization in cultured and native human retinal pigment epithelium.

The aim of this study was to determine transthyretin subcellular localization in cultured and native human retinal pigment epithelium. Monoclonal and polyclonal antibodies directed against human plasma transthyretin were used to detect transthyretin-specific immunoreactivity in cultured human retinal pigment epithelium. At the light microscopic level, transthyretin-specific immunoreactivity was observed throughout the cytosol with intense perinuclear staining. Nuclear staining was faint, but detectable. Both monoclonal and polyclonal antibodies exhibited similar staining patterns. An electron microscopic immunogold labeling protocol detected transthyretin-specific immunoreactivity in cultured and native human retinal pigment epithelium. Transthyretin-specific immunogold labeling within mitochondrial, apical, basal, nuclear and cytosolic subcellular compartments was quantitated and statistically analyzed. The pattern of transthyretin labeling was similar for each antibody, and comparable between cultured and native human retinal pigment epithelium. Transthyretin labeling was observed in mitochondrial and nuclear compartments, and in close apposition to both apical and basal membranes. Transthyretin labeling density was highest in the mitochondrial compartment and was significantly greater than labeling in all other compartments. Detection of transthyretin labeling in mitochondrial and nuclear compartments suggests an intracellular role for transthyretin in human retinal pigment epithelium, possibly as a cytoplasmic carrier protein for thyroxine.

Aged↗
PubMed2000

Creatine kinase in human retinal pigment epithelium.

Retinal pigment epithelial ion transport activity, and consequent ATP consumption vary significantly as a function of photoreceptor activity. In a variety of cell types, ATP levels are maintained during high-energy usage by phosphocreatine hydrolysis, catalysed by the enzyme creatine kinase. The present work was designed to assess the importance of creatine kinase in retinal pigment epithelial cell metabolism. To this end, activity measurements, non-denaturing gel electrophoresis, Western blot analysis and immunohistochemistry were used to characterize creatine kinase in retinal pigment epithelium. Total creatine kinase activity in the retinal pigment epithelium is approximately 0.05 micromol ATP mg protein(-1) min(-1). The bulk of this activity was mediated by the B-CK isoform. However, by immunoblotting, non-denaturing gel electrophoresis and immunohistochemistry, the presence of the M-CK isoform of creatine kinase was also detected. The M-CK isoform was plasma membrane associated and predominately localized to the apical surface. Creatine kinase in the retinal pigment epithelium could function in a spatial energy shuttle that helps to sustain apical plasma membrane ion transport activity.

Blotting, Western↗
PubMed1989

Effect of lifelong selenium and vitamin E deficiency or supplementation on pigment accumulation in rat peripheral tissues.

The accumulation of lipopigments during aging in several peripheral organs and in the nervous system is considered to be related to the peroxidation of unsaturated fatty acids. In this study the effect of lifelong (until to 18 months) dietary antioxidants selenium and vitamin-E on pigment accumulation in some peripheral tissues was estimated using fluorescence and electron microscopy. In the vitamin E deficiency group, there was increased pigment accumulation in all peripheral tissues studied except the hypogastric ganglion, where no change was observed. The vitamin E supplementation degreased the pigment accumulation in older animals in some of the tissues studied. At the electron microscopical level the accumulated pigment in the adrenal cortex showed a lipofuscin-like structure. Lifelong selenium supplementation or deficiency did not significantly alter pigment accumulation in any of the tissues studied. It is possible that in many organs dietary selenium may not play a critical role in lipofuscin formation.

Adrenal Glands↗
PubMed1976

Differences in black pigmentation in lepidopteran cuticles as revealed by light and electron microscopy.

Black cuticles of larvae and pupae from various Lepidoptera were studied by light and electron microscopy. There are striking differences in the representation of black pigmentation, especially at the ultrastructural level. Two types may be described: 1. With the light microscope black melanin-like grana, electron-dense electron microscopically, are found in the distal parts of the exocuticle. This type is demonstrated in larvae of Celerio euphorbiae, Papilio machaon, and Phalera bucephala. 2. With the light microscope, a dark homogeneous layer in the distal exocuticle can be recognized, however, electron microscopically no structures correlated with this dark pigment layer. This type of pigmentation was present in pupae of Pieris brassicae and Aglais urticae; in Pieris larvae the dark pigmented layer appeared to be limited to the epicuticle. In Celerio processes of the epidermal cells are involved in transporting precursors to the exocuticle. The conclusion was reached that black pigmentation in cuticles is based on different mechanisms as proposed by structural features. The two likely mechanisms are melanization and sclerotization.

Animals↗
PubMed1979

Hybrid pigment organelles in an invertebrate.

Observations of a number of vertebrate chromatophores have revealed the presence of more than one type of pigment organelles, suggesting that the different types are all derived from an equipotential organelle able to differentiate into any of the major pigment-containing organelles (Bagnara, 1972). Observations are presented concerning the occurrence of hybrid pigment inclusions, i.e., all kinds of intergrades between melanosomes, pterinosomes, and reflecting platelets in pigment cells of the daddy-long-legs. It therefore seems possible that pigment organelles in some invertebrates may also be derived from a common pluripotential primordial organelle.

Animals↗
PubMed1977

The pigment architecture of the human occipital lobe.

With the aid of steromicroscopical examination of pigment preparations uo to 1,000 micronm thick the various areas of the occipital lobe of the human brain are described. In the occipital lobe there are three main cortical types, forming the striate, the parastriate area, and the peristriate zone. The parastriate area is a horseshoe-shaped fringe area adjacent to the primary visual field. It is conspicuously marked by a relatively dark stripe of pigmented granule cells dividing the fourth layer into a light upper, a pigmented middle, and a light lower zone, a unique feature of the parastriate area, which is not to be found in any other isocortical area. This three-fold layer disappears abruptly as one passes from the parastriate to a peristriate area, permitting the definitive determination of this boundary. The peristriate zone is quite large in the inferior and the lateral parts of the occipital lobe and comparatively small in the superior parts. Its peripheral boundaries do not coincide with the limits of the occipital lobe. Parts of the cuneus on the one side are covered by parietal and temporal areas, whereas peristriate areas on the other side penetrate widely into the temporal lobe along the medial occipitotemporal and to a lesser extent the parahippocampal gyrus. As regards pigment architecture, the peristriate zone is divisble into ten areas. A relatively simply organized area accompaines the parastriate area. The structure of the cortex changes gradually until one reaches the various fringe areas adjacent to the parietal and temporal areas. The limit adjoining the temporal areas is sharply traceable, since the lower of two light cortical stripes vanishes abruptly when passing from a peristriate to a temporal area. The most highly developed field, the area peristriata magnopyramidalis, occupies part of the inferolateral margin of the occipital lobe. It displays a wealth of large pyramids in the lower reaches of the third layer, which contain tightly packed and densely stained pigment granules forming large rounded aggregates in the basal cytoplasm. Pyramids of this type give the field a close resemblance to association fields such as the posterior speech area, where they are commonly encountered as the predominant neurons of the third layer.

Aged↗
PubMed1977

Intercellular gap junctions in the developing retina and pigment epithelium of the chick.

Gap junctions are found in the pigment epithelium, between retina and pigment epithelium and in the retina of 5-14 day chick embryos, they are identified using block staining and extracellular tracer techniques. In the pigment epithelium gap junctions are found between cell bodies and interdigitating processes and many change their position during development. Gap junctions between retina and pigment epithelium are only made by undifferentiated retinal ventricular cells and may provide intercytoplasmic pathways important for photoreceptor differentiation. Retinal gap junctions are found in an outer zone next to the pigment epithelium and inner zone near the vitreous, they are only seen between ventricular cells but may provide pathways for ganglion cell specification. The role of gap junctions in the generation of retinal neurons is discussed.

Animals↗
PubMed1991

Müller glia endfeet, a basal lamina and the polarity of retinal layers form properly in vitro only in the presence of marginal pigmented epithelium.

Dissociated embryonic chicken retinal cells regenerate in rotary culture into cellular spheres that consist of subareas expressing all three nuclear layers in an inside-out sequence (rosetted vitroretinae). However, when pigmented cells from the eye margin (peripheral retinal pigment epithelium) are added to the system, the sequence of layers is identical with that of an in-situ retina (laminar vitroretinae). In order to elucidate further the lamina-stabilizing effect exerted by the retinal pigment epithelium, we have compared both systems, laying particular emphasis on the ultrastructure of the basal lamina and of Müller glia processes. Ultrastructurally, in both systems, an outer limiting membrane, inner segments of photoreceptors and the segregation of cell bodies into three cell layers develop properly. Synapses are detectable in a premature state, although only in the inner plexiform layer of laminar vitroretinae. Although present in both systems, radial processes of juvenile Müller glia cells are properly fixed at their endfeet only in laminar vitroretinae, since a basal lamina is only expressed here. Large amounts of laminin are detected immunohistochemically within the retinal pigment epithelium and along a basal stalk that reaches inside the laminar vitroretinae. We conclude that the peripheral retinal pigment epithelium is essential for the expression of a basal lamina in vitro. Moreover, the basal lamina may be responsible both for stabilizing the correct polarity of retinal layers and for the final differentiation of the Müller cells.

Animals↗
PubMed1992

Biogenesis of myeloid bodies in regenerating newt (Notophthalmus viridescens) retinal pigment epithelium.

Myeloid bodies are believed to be differentiated areas of smooth endoplasmic reticulum membranes, and they are found within the retinal pigment epithelium in a number of lower vertebrates. Previous studies demonstrated a correlation between phagocytosis of outer segment disc membranes and myeloid body numbers in the retinal pigment epithelium of the newt. To test the hypothesis that myeloid bodies are directly involved in outer segment lipid metabolism and to further characterize the origin and functional significance of these organelles, we examined the effects on myeloid bodies of eliminating the source of outer segment membrane lipids (neural retina removal) and of the subsequent return of outer segments (retinal regeneration) in the newt Notophthalmus viridescens. Light- and electron-microscopic analysis demonstrated that myeloid bodies disappeared from the pigment epithelium within six days of neural retina removal. By week 6 of regeneration, rudimentary photoreceptor outer segments were present but myeloid bodies were still absent. However, at this time, the smooth endoplasmic reticulum in some areas of the retinal pigment epithelial cells had become flattened, giving rise to small (0.5 micron long), two-to-four layer-thick lamellar units, which are myeloid body precursors. Small myeloid bodies were first observed one week later at week 7 of retinal regeneration. This study revealed that newt myeloid bodies are specialized areas of smooth endoplasmic reticulum. It also showed that a contact between functional photoreceptors and the retinal pigment epithelium is essential to the presence of myeloid bodies in the epithelial cells.

Animals↗
PubMed1976

The distribution of intercellular gap junctions in the developing retina and pigment epithelium of Xenopus laevis.

The distribution of gap junctions in the developing retina and pigment epithelium of Xenopus has been examined from optic vesicle to photoreceptor outer segment stages. In the retina and pigment epithelium walls of the optic vesicle gap junctions are found between ventricular cells in the apical contact zone and close to the outside wall; a neural tube type of distribution. Optic cup formation brings the retina and pigment epithelium into contact and gap junctions form between them. After the stage of retinal specification gap junctions, previously more numerous dorsally, are more often found in the ventral retina and pigment epithelium. They continue to be found in the retinal centre between ventricular cell processes in the apical contact zone and near the vitreal basement lamella above the ganglion cell layer until stage 35. Gap junctions are occasionally made by ganglion cells and their axons, providing possible pathways initiating cell differentiation. After stage 35 gap junctions seem to be confined to the peripheral rim of the eye cup where new cells are formed throughout larval life. The observed distribution suggests that gap junctions may provide intercytoplasmic pathways for retinal specification intrinsic to the retina and pigment epithelium.

Animals↗
PubMed1981

Photoreceptor outer segment and retinal pigment epithelium in vitamin E deficient rats. An electron microscopic and electron histochemical study.

The photoreceptor outer segments and retinal pigment epithelium of vitamin E deficient rats were examined by electron microscope using electron histochemical techniques. In rats fed a vitamin E deficient diet for more than 6 months starting 20 days after birth, the photoreceptor outer segment showed vesiculation of the discs near the apical portion of the retinal pigment epithelium. In the retinal pigment epithelium, secondary lysosomes were increased in number. Reaction products of acid phosphatase activity were located in secondary lysosomes in the retinal pigment epithelium and on the disc membranes of the photoreceptor outer segment. These alterations became more prominent with the duration of vitamin E deficiency. It was assumed that the disc degeneration of the photoreceptor outer segment might be due to enhanced activity of lysosomal enzymes in the retinal pigment epithelium and the effect of released lysomal enzymes on the photoreceptor outer segment.

Animals↗